1. Field of the Invention
The present invention relates to a method for forming an image, where a direct positive color image is obtained by image-wise exposing direct positive silver halide photographic light-sensitive materials and by subjecting the materials to a color developing process in the presence of a nucleating agent and/or fogging exposure.
2. Description of the Prior Art
Photographic methods whereby a direct positive color image is obtained without necessitating a reversal processing step or negative film have well been known.
Methods used for forming a positive image using direct positive silver halide photographic light-sensitive materials which methods have hitherto been known may mainly be classified into two types taking practical usefulness into account except for special methods therefor.
One type is a method where a direct positive image is obtained after development by using prefogged silver halide emulsions and by destroying fog nuclei (latent image) in the exposed area utilizing solarization, Harschel effects and the like.
The other type is a method where a direct positive image is obtained by using unfogged internal latent image type silver halide emulsions and by image-wise exposing the emulsions and then conducting surface development after or while conducting fogging process. In the foregoing, the internal latent image type silver halide photographic emulsion means such a type of silver halide photographic emulsion having light-sensitive specks mainly inside the silver halide grains that latent images are mainly formed inside the grains by exposure.
The latter type methods give a positive image in a high sensitivity in general and thus are fit for uses where high sensitivity is required. The present invention relates to the latter type methods.
Various techniques have hitherto been known in this technical field. Main such techniques are disclosed, for example, in each specification of U.S. Pat. Nos. 2,592,250, 2,466,957, 2,497,875, 2,588,982, 3,317,322, 3,761,266, 3,761,276 and 3,796,577, and U.K. Pat. Nos. 1,151,363, 1,150,553 and 1,011,062.
Photographic light-sensitive materials of relatively high sensitivity as direct positive type can be prepared by using these known methods.
Further, the mechanism of direct positive image formation is disclosed in detail, for example, in T. H. James, The Theory of The Photographic Process vol. 4, chapter 7, pages 182 to 193, U.S. Pat. No. 3,761,276 and the like. According to the disclosures, it is believed that fog nuclei are formed selectively on the surface of the silver halide grains of unexposed areas based on a surface desensitizing action because of internal latent images (positive hole) formed by the first image-wise exposure, and then a photographic image (direct positive image) is formed on the unexposed areas by conducting a usual so-called surface developing process.
In the above-mentioned, as methods for selectively forming fog nuclei, a method generally called "light fogging method" wherein the second exposure is given on the whole surface of the light-sensitive layers (for example, U.K. Pat. No. 1,151,363) and a method generally called "chemical fogging method" wherein nucleating agents are used have been known. The latter method is disclosed in, for example, Research Disclosure, vol. 151, No. 15,162 (published in November, 1976), pages 76 to 78.
A direct positive color image may be formed by conducting surface color developing of internal latent image type silver halide light-sensitive materials after or while they are subjected to fogging process, and thereafter subjecting then to bleaching and fixing processes or bleach-fixing process. Water washing and/or stabilizing process are generally conducted after bleaching and fixing processes.
Various methods have hitherto been developed for making development speed and color forming rate of a color developing solution faster. Especially, it is necessary that a color developing agent itself is taken into oil drops in which couplers are dispersed, when an oxidized color developing agent is finally coupled with the coupler to form a dye, and various additives as additives for hastening its permeation and promoting coloring have been known. As such as additive exhibiting especially great coloring promoting effect, benzyl alcohol has hitherto been known and used for process of various color photographic light-sensitive materials and are widely used now.
Benzyl alcohol is very low in water solubility, and thus to use diethylene glycol, triethylene glycol or alkanolamine have been widely used in order to enhance its solubility.
However, when waste water containing these compounds and benzyl alcohol itself is processed, a problem arises that load for environmental pollution countermeasure is large because of high BOD and COD values of the waste water. Therefore, in spite of above-mentioned advantages such as improvement of coloring property and solubility thereby, it has been desired to reduce or remove benzyl alcohol from the viewpoint of waste water process.
Further, solubility of benzyl alcohol is still inadequate even when the aforementioned solvent such as diethylene glycol is used, and it was a cause of bringing load in labor and time for preparing developing solution.
Further, when benzyl alcohol is brought about with the developing solution in the subsequent bleaching bath or bleach-fixing bath and accumulated, a certain kind of coupler forms a leuco dye, which is a cause of lowering color density. Further, accumulation of benzyl alcohol makes washing out the components of the developing solution, above all the color developing agents inadequate, and as a result, image preservability owing to the remaining color developing agents are sometimes deteriorated.
From the above various view, it has been desired to reduce or remove benzyl alcohol from a color developing solution.
The color laboratory industry has these problems on the one hand, and is also driven by necessity of shortening process time on the other hand because of strong request for shortening the period for finishing of a print.
However, it is apparent that color density will remarkably be lowered if development time is shortened and benzyl alcohol is removed from the color developing solution. Thus, these requests cannot simultaneously be satisfied according to the conventional art.
Further, in usual chemical fogging methods, effect of the nucleating agent is obtained only at a high pH of 12 or more. However, deterioration of the developing agent is liable to occur because of air oxidation in such a high pH condition and unstable, and as a result development activity is remarkably lowered. Furthermore, usual chemical fogging methods take a long time for processing because development speed is slow, and especially when a developing solution of a low pH is used, they take a much longer time for processing.
In case of light fogging methods, a high pH condition is not required and thus the method is relatively advantageous in practical use. However, various technical problems should be solved in order to utilize the method for various purpose in comprehensive photographic fields. That is, as light fogging method is based on formation of fog nucleus by photolysis of silver halide, appropriate exposure illuminance and exposure intensity therefor changes depending on the kind and property of silver halide to be used. Therefore, there is a problem that it is difficult to conduct a constant photofinishing and further, development apparatus is complicated and expensive.
Thus, it has been difficult in both the usual fogging methods to obtain a good direct positive image. As a means for solving the problem, compounds exhibiting a nucleating action even at pH 12 or below have been proposed in Japanese Published Unexamined Patent Application No. 69613/1977 and U.S. Pat. Nos. 3,615,615 and 3,850,638. However, these nucleating agents act on silver halide or they themselves decompose during preservation of the light-sensitive materials before process. Thus, there is a defect in the nucleating agents that they after all lower the maximum image density after processing.
U.S. Pat. No. 3,227,552 discloses to raise development speed at medium concentration using a hydroquinone derivative. However, development rate was not adequate even by use of the compound, and especially only an inadequate development rate was obtained in case of a developing solution of pH 12 or less.
Further, Japanese Published Unexamined Patent Application No. 170843/1985 discloses that maximum image density is raised by adding a mercapto compound having a carboxyl or sulfo group. However, the effect obtained by the addition of these compounds is small. Moreover, pH value of the developing solution is 12.0 and thus stability of the developing solution is inadequate.
Japanese Published Unexamined Patent Application No. 134848/1980 discloses that the formation of a rereversal nagative image is prevented by processing the materials in the presence of a nucleating agent with a processing solution (pH 12.0) containing a tetrazaindene compound to lower the minimum image density. However, this method does not increase the maximum image density and development rate.
Japanese Published Examined Patent Application No. 12709/1970 discloses that a triazoline-thion or tetrazolinethion compound is added as an antifoggant to a light-sensitive material capable of forming a direct positive image in a light fogging method. However, even these method could not attain a high maximum image density and fast development rate.
As apparent from the foregoing, there have even been no techniques that gives a direct positive color image having a high maximum color image density and low minimum color image density constantly by processing the material in a short time using a color developing solution of a low pH, i.e. pH 12 or less.
Further, there is a problem that the higher speed of a direct positive emulsion the greater the formation of rereversal negative image in exposure under a high illuminance.